A Comparative Study of Microstructure and Residual Stresses of CMT-, MIG- and Laser-Hybrid Welds

Abstract:

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Recently a new welding technique, the so-called ‘Cold Metal Transfer’ (CMT) technique
was introduced, which due to integrated wire feeding leads to lower heat input and higher
productivity compared to other gas metal arc (GMA) technique. Here microstructure formation and
residual stress state in aluminum CMT welds are characterized and compared to those produced by
pulsed MIG- and Laser-hybrid techniques. The results show a small heat affected zone (HAZ) in the
MIG weld, the HAZ in the CMT and the laser hybrid welds was not visible by optical and scanning
electron microscopy. Compared to the MIG welding the CMT process appears to introduce slightly
smaller maximum tensile residual stresses into the weld.

Abstract: Recently a new welding technique, the so-called ‘Cold Metal Transfer’ (CMT) technique
was introduced, which due to integrated wire feeding leads to lower heat input and higher
productivity compared to other gas metal arc (GMA) techniques. Here microstructure formation and
residual stress state in dissimilar steel to aluminum CMT welds are investigated. The intermetallic
phase seam between the filler and the steel is only a few micrometers thick. Residual stress analyses
reveal the formation of the typical residual stress state of a weld without phase transformation. Both
in longitudinal and in transversal direction compressive residual stresses exist in the steel plate
parent material, tensile residual stresses are present in the heat affected zone of the steel and the
aluminum alloy. The area containing tensile residual stresses is larger in the aluminum alloy due to
its higher heat conductivity than in the steel. Due to the symmetry in the patented voestalpine
welding geometry and the welding from bottom and face side of the weld, the residual stress
distributions at the top and at the bottom side of the weld are very similar.